The plausible mechanisms of tramadol for treatment of COVID-19.

Currently, no single medication has been approved for the management of coronavirus disease-2019 (COVID-19) caused by the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Therefore, drug repositioningby investigating the use of existing drugs for management of COVID-19 patients is considered a desperate need. Tramadol is a commonly prescribed analgesic drug for treatment of moderate to severe pain with less potential for dependence and respiratory depression. Multiple evidence support that tramadol is a promising drug for treatment of COVID-19 patients. Herein, we discuss the possible beneficial effects of using tramadol against SARS-CoV-2 infection and their underlying mechanism of action. The anti-inflammatory effect of tramadol may help to suppress the COVID-19 related cytokine storm through decreasing interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α), and C-reactive protein (CRP). Besides, tramadol activates natural killer (NK) and T-cells and enhances IL-2 secretion, which produce immune-enhancing effect against SARS-CoV-2. Recent studies confirmed that COVID-19 patients with acute respiratory failure showed increased fibrin formation and polymerization that may lead to thrombosis. Tramadol owing to its hypocoagulable effect may protect against venous thromboembolism in these patients. Moreover, tramadol can exert a cardioprotective effect via decreasing lactate dehydrogenase (LDH) level which is elevated in most of patients with COVID-19. Furthermore, the severity and mortality of COVID-19 have been correlated with old age patients, which may be due to the lack of antioxidant mechanisms and increased oxidative damage. Tramadol could protect COVID-19 patient from disease complications by increases the antioxidant enzymes superoxide dismutase and glutathione peroxidase while diminished malondialdehyde. More interestingly, tramadol as an effective analgesic and antitussive may have a beneficial effect on COVID-19 patients suffering from cough, headache, ache, and pain. The tramadol anti-psychotic effect may also protect against psychiatric disorders associated with SARS-CoV-2 infection. Moreover, tramadol has bactericidal activity against a wide range of pathogens including Pseudomonas aeruginosa which is common in severe COVID-19 patients leading to pneumonia with worse clinical outcomes. Therefore, we hypothesize that tramadol might be a promising adjuvant therapeutic option against SARS-CoV-2 infection. Based on that, tramadol should be considered as adjuvant therapy for COVID-19 clinical trials.